Panniers v Backpack for 3day epic

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We are doing a 3 day ride in the Cairngorms, Scotland staying overnight in B&B's (Aviemore-Tomintoul-Braemar-Blair Athol). The route is nearly entirely off-road over relatively challenging terrain. Unsure whether it is preferable to use a backpack or mount panniers on my bike. Mounting panniers is not that straightford as have no fittings for a rack (Cotic Soul, steel hardtail) so would need to put clips in my bike (I believe P-clips (?) are whar are needed to fit the rack). Alternatively, as I dont have to carry any camping kit, was going to buy a backpack e.g. Deuter Trans Alpine 26, which is designed specifically for biking. Any comments or guidance?

We are doing a 3 day ride in the Cairngorms, Scotland staying overnight in B&B's (Aviemore-Tomintoul-Braemar-Blair Athol). The route is nearly entirely off-road over relatively challenging terrain. Unsure whether it is preferable to use a backpack or mount panniers on my bike. Mounting panniers is not that straightford as have no fittings for a rack (Cotic Soul, steel hardtail) so would need to put clips in my bike (I believe P-clips (?) are whar are needed to fit the rack). Alternatively, as I dont have to carry any camping kit, was going to buy a backpack e.g. Deuter Trans Alpine 26, which is designed specifically for biking. Any comments or guidance?
If you can truly minimize your load, then a backpack could work. If you insist on carrying a full outfit for everyday, then I would consider the panniers as a comfort issue.